This invention relates to pressure sensitive adhesives compositions. More particularly, the invention relates to pressure sensitive adhesive compositions comprising terpolymers of ethylene, vinyl acetate and di-2-ethylhexyl maleate or the corresponding fumarate.
Pressure-sensitive adhesives, especially those which are normally used in the form of adhesive tapes or veneers and wallpapers, have attained considerable industrial importance. Their function is to provide instantaneous adhesion when applied under light pressure, and most applications further require that they can be easily removed from the surface to which they have been applied by a light pull. They are characterized by having a built-in capacity to secure this instantaneous adhesion to a surface without activation, such as treatment with solvents or heat, and also by having sufficient internal strength so that the adhesive material will not rupture before the bond between the adhesive material and the surface ruptures. The capacity to obtain instantaneous adhesion is usually expressed as the amount of "tack" or "tackiness". Ordinarily it is desirable to obtain as much tack as possible without losing a significant amount of internal strength (cohesion). The latter balance of adhesive and cohesive properties has been difficult to obtain in adhesive polymers since monomers conventionally added to increase the cohesive strength generally result in a decrease in adhesive tack.
U.S. Pat. No. 4,322,516 issued Mar. 30, 1982 to Wiest et al. discloses copolymers for use as pressure adhesives comprising ethylene, acrylic esters, vinyl acetate and (meth) acrylamide. While providing some improvements over adhesives of the prior art, the latter copolymers are still deficient with respect to their balance of cohesive and adhesive properties, particularly when applied to hard to adhere surfaces such as the hydrophobic polyolefin substrates.